Hydrological pathways in a glaciated watershed in the catskill mountains
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Hydrological pathways in a glaciated watershed in the Catskill Mountains. Adrian Harpold. Improving our understanding of runoff processes in the Catskills. How long?. Stream chemistry is a function of 1) sources, 2) flowpaths 3) age of water.

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Improving our understanding of runoff processes in the catskills
Improving our understanding of runoff processes in the Catskills

How long?

  • Stream chemistry is a function of 1) sources, 2) flowpaths 3) age of water.

  • Variable saturated areas (VSA) are a quick source of storm runoff.

How did it get there?

  • Spatial predictions of VSA are often based on topography and soil properties.

  • Are we neglecting the effects of small-scale variability on saturated areas?

Where from?



Identifying and monitoring controls on saturation areas
Identifying and monitoring controls on saturation areas Catskills

36.8 km2

  • Soil piping creates near-stream saturated areas

  • Groundwater springs generate hillslope saturated areas

  • Overland flow, water table heights, and water chemistry are collected across the hilllsope


Response to rainfall events
Response to Catskillsrainfall events

Prior to rainfall

During rainfall

New saturated connections

to the stream channel


Connection between stream discharge and hillslope features
Connection between stream discharge and hillslope features Catskills

  • Water table shows hysteresis versus streamflow (delayed)

  • Near-stream transient GW shows least delay

  • Overland flow measurements are much more correlated to streamflow(no hysteresis)


Response of stream chemistry to rainfall
Response of stream chemistry to rainfall Catskills

Single Event

Nine Events


Identifying source areas to the stream via end member mixing analysis
Identifying source areas to the stream via end-member mixing analysis

Saturated areas respond quickly to large rainfall

Groundwater contributes 53% to 95% of runoff volume during 9 events

Saturated areas contribute 2% to 24%

Throughfall contributes 4% to 25%

Rain response is delayed and damped

Groundwater

dominates baseflow


Effects of hillslope processes on stream response for nine rainfall events

Near-stream saturation areas active analysis

Effects of hillslope processes on stream response for nine rainfall events

  • Contributions from VSA are dependent on antecedent conditions

Hillslope saturation areas connected (maximum contributing area achieved)

  • Large storm runoff volumes have similar VSA contributions

  • Contributions from rainfall control the peak runoff for each event.

Hillslopes begin to throughfall to stream (maximum contributing area achieved)


Conceptualizing source areas and flowpaths in a glaciated watershed
Conceptualizing source areas and flowpaths in a glaciated watershed

Prior to rainfall

  • Previous conceptualization: saturated areas grow in extent from the toe of the hillslope up.

  • Alternative conceptualization: saturated areas near the stream are connected to discrete hillslope saturated areas.

  • Maximum saturation contribtuions are limited by the ‘quick’ draining preferential flowpaths.

During rainfall


Conclusions
Conclusions watershed

  • Subsurface variabilities (e.g. groundwater springs and soil piping) can cause persistent spatial patterns of surface saturation, even during very dry periods.

  • Expansion of near-stream saturated areas are a source of runoff in smaller storms (<7 mm), but hillslope saturation areas contribute regularly in larger events.

  • After the maximum saturation extent has been reached, additional rainfall contributes throughfall to the stream.


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